Pressure-responsive fluid controlling system

ABSTRACT

A pressure responsive fluid control system for an air tool which is effective to shut off the tool when it reaches a predetermined torque and motor back pressure but will not prematurely react to temporary pressure increases caused by motor inertia. A back pressure sensitive valve has a face exposed to a fluid accumulator chamber whose volume is sufficient to absorb temporary pressure surges but which will increase in pressure to close the valve when the predetermined torque and back pressure are attained.

United States Patent [72] Inventor John A. Borries Chesterland, Ohio [21] AppI. No. 47,196- [22] Filed June 18, 1970 [45] Patented Sept. 28, 1971 [73] Assignee Cooper Industries, Inc,

Houston, Tex.

E [54] PRESSURE-RESPONSIVE FLUID CONTROLLING SYSTEM 4 Claims, 4 Drawing Figs. [52] U.S. Cl 173/12, 91/59 [5 I] B25b 23/14 [50] Field ofSearch 91/59; 173/12 [56] References Cited UNITED STATES PATENTS 3,373,824 3/1968 Whitehouse 173/12 3,505,928 4/I970 Whitehouse I73/I2 X Primary Examiner-Ernest R. Purser Attorney-0wen & Owen ABSTRACT: A pressure responsive fluid control system for ;an air tool which is effective to shut off the tool when it reaches a predetermined torque and motor back pressure but will not prematurely react to temporary pressure increases 1 caused by motor inertia. A-back pressure sensitive valve has a face exposed to a fluid accumulator chamber whose volume is sufficient to absorb temporary pressure surges but which will increase in pressure to close the valve when the predetermined torque and back pressure are attained.

PRESSURE-RESPONSIVE FLUID CONTROLLING SYSTEM BACKGROUND OF THE INVENTION In tools activated by air-driven motors it is often desirable to provide a pressure sensitive fluid flow controlling device which will automatically control the flow of air to the tool. This invention relates to an improved automatic controlling device for such air-driven tools as nut setters, screwdrivers and the like. 7

In pressure-responsive fluid controlling devices for air driven tools, it has been common to provide a valve sensitive to a predetermined back pressure caused by a work load placed upon the tool air motor. A fluid controlling device of this type is illustrated in U.S. Pat. No. 3,373,824 to Hugh L. Whitehouse.

An inherent problem in these conventional controlling devices is the sensitivity of the flow controlling valve to a back pressure buildup caused by the inertia of the air-driven motor when the tool is first activated. This starting back pressure, in the absence of some inhibiting means, will cause the controlling device to react prematurely and render the operation of the tool impossible.

The aforementioned Whitehouse patent avoids starting back pressure buildup through the use of a tapered, manually operated throttle valve. In that device, if the throttle valve is first cracked open and then gradually opened to admit maximum line airflow, the back pressure will not surge significantly enough to activate the controlling valve. This type of inhibiting device of course depends upon the skill of the tool operator and even if properly used, is slow in starting the tool.

It is accordingly the object of the present invention to provide a back pressure, sensitive fluid control valve which will not be prematurely activated by initial surges caused by air motor inertia.

It is a further object of the present invention to provide a means by which the operation of an automatic control valve is completely independent of the tool operator and thus not subject to operator errors.

SUMMARY OF THE INVENTION These and other objects are accomplished by the present invention which includes a control valve, movable from an open to a closed position within a valve chamber, comprises a valve piston having a main line passage in fluid communication with an inlet port and an outlet port in the valve chamber when the valve is in its open position. The outlet port is in fluid communication with an air-driven motor. The valve piston comprises a head and a secondary piston head protruding from said head into an orifice in the base of the valve chamber, which orifice opens into an accumulator chamber. The valve piston is urged into its open position by a biasing spring. The accumulator chamber is in fluid communication with the valve outlet port through a restricted back pressure inlet and has a volume substantially larger than the volume of the back pressure inlet and the outlet port. Fluid flow through the back pressure inlet is thereby impeded and the corresponding pressurization rate of the larger accumulator chamber is shower than the pressurization rate of the outlet port. Air is admitted to said air-driven motor through the main line passage of the valve piston when said valve is in its open position. Due to inertia of the driven tool when said air motor is started, airflow through the main line passage and the outlet port is initially restricted. This temporarily restricted airflow creates a back pressure surge which pressurizes the accumulator chamber through said back pressure inlet at a rate slower than the surge rate at said outlet port. The back pressure in the accumulator chamber urges against the secondary piston head of said valve, but since the surge in said accumulator chamber is only temporary and increases at a rate slower than the back pressure increase at said outlet port (thus never reaching the maximum surge pressure reached at said outlet port) the biasing spring maintains said valve in its open position. However as the air motor meets increasing resistance (caused, for example, by increased torque loads on the air-driven tool) and thus back pressure increases at said outlet port, the accumulator pressure on said secondary piston head will increase to the point that said biasing spring is overcome thereby causing said valve piston to move toward its closed position. As said piston moves, a line inlet or holding port from said inlet The control valve is thus responsive to a predetermined back pressure but is not responsive to starting pressure surges which tend to close said valve prematurely. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of an air-driven motor, a fluidcontrolling device embodying the invention, and a throttle valve;

FIG. 2 is a view in elevation of an air-driven motor with a fluid-controlling device embodying the invention and a throttle valve, showing the controlling valve in closed position;

FIG. 3 is an elevational view similar to FIG. 2 but showing the controlling valve in open position;

FIG. 4 is a graph illustrating the operational characteristics of the present invention in connection with a torque-responsive air-driven tool. DESCRIPTION OF A PREFERRED EM- BODIMENT Referring to FIGS. 1, 2 and 3, a pressure responsive fluidcontrolling valve 10 is shown. The valve 10 comprises a closed valve chamber 11 having an inlet port 12 and an outlet port 13, and a valve piston 14 movable within the valve chamber 11 from an open to a closed position. The valve piston 14 comprises a piston body 15 having a main line passage 16 in fluid communication with the inlet port 12 and the outlet port 13, a head 17, and a secondary piston head 18 protruding from the head 17 through an orifice 19 in an orifice plate 20, into an accumulator chamber 21 when the valve piston 14 is in its open position. The outside diameter of the secondary piston head 18. fits closely within the inside diameter of the orifice 19. The valve piston 14 is urged towards its open position by a bias spring 22 which is tensioned by an adjustable bias spring plug 23.

The accumulator chamber 21 is in fluid communication with the outlet port 13 through a restricted back pressure inlet 24. The volume of the back pressure inlet 24 is substantially less than the volume of the accumulator chamber 21 and the volume of the outlet port 13. Fluid flow through the back pressure inlet 24 from the outlet port 13 is thereby significantly restricted. Furthermore, because of the dimensional relationship of the accumulator chamber 21 to the restricted inlet 24, changes in air pressure in the outlet port 13 will occur at a rate faster than corresponding changes in pressure in the 21 due to the impeded flow through the restricted inlet 24.

Air from a pressurized source is introduced through the inlet port 12, the mainline passage 16 and the outlet port 13 to an air-driven motor 25 when the valve 10 is in its open position as shown in FIG. 3. As an increasing work load (e.g. increased torque resistance) is placed upon the air-driven motor -25, airflow through the motor 25 is impeded causing a corresponding back pressure increase at the outlet port 12 and in the accumulator chamber 21. As back pressure in the accumulator chamber 21, urging against the secondary piston head 18, increases sufficiently to overcome the force of the bias spring 22, the valve piston 14 begins to move toward its closed position. (The initial-movement of the valve piston 14 places the piston head 17 in communication with the pressure in the chamber 21). Because the pistonhead 17 has a greater crosssectional area than the secondary piston head 18, the valve piston 14 is under more force once said pistonhead 17 is thus exposed to the chamber 21. The valve piston 14 is thereby snapped towards its closed position, closing the mainline passage 16 between the inlet port 12 and the outlet port 13. As soon as the piston moves far enough to uncover a holding port 26, it is further urged towards and held in closed position by line pressure.

Now referring to FIG. 4 the operation of a torque responsive fluid controlling valve embodying the invention is illustrated on a graph. When air under pressure is admitted to the air motor 10, the inertia of the motor 25 initially impedes air flow, causing a back pressure surge, the peak of which is indicated on the motor back pressure curve at point a. Because the accumulator chamber 21 is in communication with the outlet port 13 through the restricted back pressure inlet 24, the chamber 21 is correspondingly pressurized by the back pressure surge, but at a significantly slower rate as shown on the pressure accumulator chamber curve. Due to this time-lag in pressurization of the accumulator chamber 21 and due to the relatively large volume of the accumulator chamber 21, the accumulator pressure remains below the motor back pressure when the back pressure increase is only momentary. Thus by setting the bias spring 22 at a resistance above the accumulator pressure achieved during a starting surge, the valve piston 14 will not respond to this temporary back pressure increase. At the same time however, when sustained torque resistance, as shown on the torque curve, is applied to the airdriven motor 25, pressure in the accumulator chamber 21 will eventually increase to the point of overcoming the resistance of the bias spring 22 as shown at point b. When a predetermined back pressure valve in the accumulator chamber 21 is reached, such as valve at point b, the control valve will automatically respond as previously explained.

The fluid-controlling valve 10 is thereby insensitive to sudden temporary increases in back pressure which would cause premature operation of said valve 10, but is fully responsive to predetermined pressures achieved through sustained loads on the air-driven motor 25.

It will be apparent that a range of predetermined pressures at which the tool responds, and thus a range of ultimate torque value, may be attained by adjusting the spring bias by turning the bias spring plug 23. The lower limit of the range must remain above the maximum starting back pressure surge in the accumulator chamber 21 to avoid premature operation of the valve. That is, the pressure at point b must exceed that achieved at point e in FIG. 4. Thus, for a given range of operating characteristics, the size relationship between the chamber 21, the restricted back pressure inlet port 24 and the outlet port 13 may be constant. Other advantages of the above described system will be apparent to those skilled in the art and may be made without departing from the scope of the following claims.

lclaim:

1. A control system for a tool driven by fluid under pressure effective to shut-off said tool when a predetermined back pressure is encountered by said control system caused by said tool encountering a predetermined load, but not responsive to momentary back pressure surges of less than said predetermined back pressure, said control system comprising, in combination, a fluidtight valve housing, a fluid inlet port connecting a fluid pressure source to said housing, a fluid outlet port from said housing connected to an air motor driving said tool, a valve piston within said housing movable between (1) an open position at which fluid may pass from said inlet port through said housing to said outlet port and (2) closed position at which communication between said inlet and outlet shut-off said tool when a predetermined back pressure is encountered by said control system caused by said tool encountering a predetermined load, but not responsive to momentary back pressure surges of less than said predetermined back pressure, said control system comprising, in combination, a fluidtight valve housing, a fluid inlet port connecting a fluid pressure source to said housing, a fluid outlet port from said housing connected to an air motor driving said tool, a valve piston within said housing movable between (1) an open position at which fluid may pass from said inlet port through said housing to said outlet port and (2) a closed position at which communication between said inlet and outlet valve piston to urge said piston against said bias means toward said closed position, and a holding port positioned to apply line pressure to said valve pistonhead when said valve piston reaches its said closed position whereby, when said back pressure reaches said predetermined value in accordance with the load on said tool the force of said back pressure in said accumulator on sa|d secondary pistonhead is sufficient to move said piston from its said open position to expose said valve pistonhead to said accumulator pressure and whereby continued movement of said piston toward said closed position will open said holding port such that line pressure is applied to said pistonhead to hold said piston in a closed position.

2. A control system for a tool driven by fluid under pressure according to claim 1 wherein the volume of said accumulator chamber is substantially greater than the volume of said restricted means connecting said outlet port to said chamber whereby the back pressure in said chamber achieved through said restricted means increases at a rate slower than the back pressure increase rate at said outlet port.

3. A control system for a tool driven by fluid under pressure according to claim 2 wherein said restricted means connecting said outlet port to said accumulator chamber has a volume substantially less than the volume of said outlet port whereby the back pressure in said chamber increases at a rate slower than the back pressure increase rate at said outlet port due to an impeded fluid flow rate from said outlet port into said chamber through said restricted means.

4. A pressure responsive fluid-controlling system according to claim 3 wherein said bias means includes a spring and means for adjusting the tension of said spring to maintain a pressure upon said valve piston substantially equal to a predetermined accumulator chamber back pressure.

v (PAGE 1) UNITED STATES PATEN" OFFICE CERTIFICATE OF CORRECTION Patent No. 3 ,608,647 Dated September 28, 1971 Inventofls) Jokin A, Berries 'It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below: 7

F l. I "1 1 y 4 Co-luinn 1 line 60; after :"is", the word "shower" should be "slower", n

. v r I l Column 2, ii-navy, fter the word "inlet", insert --port is placed-influid communication with the valve piston heac i, causin g said-valve p'istonto snap into its closed position, closing the main line passage to thus shut off air flow to the mot OI'I" Column? liinei" 18, efter the, insert -'-chamber--,

Column 5, line 22; after 1s",- insert "the",

I (PAGE 2) P UNITED STATES PATENT OFFICE CERTIFICATE OF CQRRECTION Patent N 3: O8:6u7 p ged Septem 97 Inv n fl John A, Berries.

- 'It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line &5 through column 4,. line 30, CANCEL the entireclaim l and substitute:

"l; A' control system-for a' tool driven by fluid under pressure effective to shut-off said tool when a predetermined back pressure is encountered by said control system caused by said tool encountering a predetermined load, but not responsive to momentary'back pressure surges of less than said predetermined back pressure, said control system comprising, in combination,

a fluid-tight valve housing, a fluid inlet port connecting a fluid pressure source ;to said housing, a fluid outlet port from said housing connected to an .air motor driving said tool, a I valve piston within said housing-movable between (1) an open position at which fluid may pass from said inlet-port through; said housing .to said outlet portand (2) a closed position at which communication between said inlet and outlet ports is shutoff, means biasing said valve piston toward its saidopen position, said valve piston having ahead and a secondary piston head of reduced area protruding from said head through an orifice plate at one end of said valve housing into an accumulator chamber, said chamber having a volumesufficient to prevent a temporary air surge from reaching said predetermined back pressure value, restricted means connecting said outlet port 'to said accumulator chamber whereby pressure therein will increase inresponse tom-increased back-pressure caused in said motor but at a rate slower than the initial back-pressure increase at the outlet 'port', said orifice plate separating said accumulator chamber from said valve piston head with its orifice closed by said secondary piston head of said valve pistonwhen in said open" position such that pressure in said accumulator chamber bears against said secondary piston of said valve piston to urge said piston against said bias means toward said closed position, and a holding port, positioned to apply line pressure to said valve piston head when said valve piston reaches its said closed position whereby, when said back-pressure reaches v (PAGE 3) Egg? 1 UNITED STATES PATENT OFFICE CERTIFICATE OF CQRRECTION Patent No. 5 6Q8 64l Dated September 28 1971 Inventor(s) John A. Berries It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

(CLAIM 1 Cont,

said predetermined ralue i'n ac'cordancewith the load on said tool, the -force of'sa'id b ack pressure in said accumulator,

on said. secondary *piston' head is sufficient to move said pistonfron'i its said open position toexpose said valve piston .headto said accumulator pressure and whereby continued movement-f of'said piston toward said closed position will open said holding "port such that line pressure is applied -to said piston head to -holdsaid piston in aclosed position."

Signed andsealed this 11th day of April 1972.

(SEAL) Attest:

EDWARD MFL TCHER 3 ROBERT GQTTSCHALK At te sting O f-ficer I I Commissioner of Patents 

1. A control system for a tool driven by fluid under pressure effective to shut-off said tool when a predetermined back pressure is encountered By said control system caused by said tool encountering a predetermined load, but not responsive to momentary back pressure surges of less than said predetermined back pressure, said control system comprising, in combination, a fluidtight valve housing, a fluid inlet port connecting a fluid pressure source to said housing, a fluid outlet port from said housing connected to an air motor driving said tool, a valve piston within said housing movable between (1) an open position at which fluid may pass from said inlet port through said housing to said outlet port and (2) a closed position at which communication between said inlet and outlet ports is shut off, means biasing said valve piston toward its said open position, said valve piston having a head and a secondary piston head of reduced area protruding from said head through an orifice plate at one end of said valve housing into an accumulator chamber, said chamber having a volume sufficient to prevent a temporary air surge from reaching said predetermined back pressure value, restricted means connecting said outlet port to said accumulator chamber whereby pressure therein will increase in response to increased back-pressure caused in said motor but at a rate slower than the initial back-pressure increase at the outlet port, said orifice plate separating said accumulator chamber from said valve pistonhead with its orifice closed by said secondary pistonhead of said valve piston when in said open position such that pressure in said accumulator chamber bears against said secondary piston of said valve piston to urge said piston against said bias means toward said closed position, and a holding port positioned to apply line pressure to said valve pistonhead when said valve piston reaches its said closed position whereby, when said back pressure reaches said predetermined value in accordance with the load on said tool, the force of said back pressure in said accumulator on said secondary pistonhead is sufficient to move said piston from its said open position to expose said valve pistonhead to said accumulator pressure and whereby continued movement of said piston toward said closed position will open said holding port such that line pressure is applied to said pistonhead to hold said piston in a closed position.
 2. A control system for a tool driven by fluid under pressure according to claim 1 wherein the volume of said accumulator chamber is substantially greater than the volume of said restricted means connecting said outlet port to said chamber whereby the back pressure in said chamber achieved through said restricted means increases at a rate slower than the back pressure increase rate at said outlet port.
 3. A control system for a tool driven by fluid under pressure according to claim 2 wherein said restricted means connecting said outlet port to said accumulator chamber has a volume substantially less than the volume of said outlet port whereby the back pressure in said chamber increases at a rate slower than the back pressure increase rate at said outlet port due to an impeded fluid flow rate from said outlet port into said chamber through said restricted means.
 4. A pressure responsive fluid-controlling system according to claim 3 wherein said bias means includes a spring and means for adjusting the tension of said spring to maintain a pressure upon said valve piston substantially equal to a predetermined accumulator chamber back pressure. 